1. Field of the Invention
The present invention relates to a rotor for a small-sized motor, which allows the end of a winding coil to be electrically well connected to the leg of a commutator with good workability, and a method of manufacturing the same.
2. Description of the Related Art
The conventional connection of each commutator piece and a winding coil end will be described by referring to FIG. 5. FIG. 5 is a perspective view of the commutator part of a small-sized motor. In the figure, reference numeral 11 denotes a shaft of the rotor, and reference numeral 22 denotes a commutator piece, and reference numeral 24 denotes a commutator core, and reference numeral 26 denotes a commutator leg. Thus, the commutator comprises each commutator piece 22 which is arranged on a resin commutator core 24, and a commutator leg 26 which is formed integrally with each commutator piece 22 at the end thereof for connecting the winding coil end. FIG. 6 is a side view of the commutator part shown in FIG. 5, and shows the state where the winding coil end is connected. The commutator leg 26 is bent to the commutator piece to hold the winding coil end as shown in the figure, and spot welding is applied.
FIG. 7 is a view showing only a varistor taken out on the right side in the figure, and showing the state where that varistor is attached and connected on the left side. In the case of a small-sized motor with a commutator, when the brush which comes into sliding contact with the commutator passes between the commutator pieces, an arc is produced, and by this arc, radio wave hindrance may be given to the communication devices, or the life of the brush may be reduced. Therefore, it is conventionally well known that a varistor is attached to the rotor of a motor as a spark quenching element. One example of such a varistor has a shape shown on the right side in FIG. 7, and totally, it is shaped like a toroidal disk, and has electrodes of the number of the rotor magnetic poles, that is, the number equal to that of the commutator pieces. Each electrode of this varistor 21 is separately soldered to each commutator leg 26. By this soldering, the varistor 21 is not only electrically connected but also mechanically fixed coaxially to the commutator.
To the wire as a conductive material which is used for electronic parts such as a winding coil of a small-sized motor, coating is usually applied with insulating materials such as polyurethane or polyester to form an insulating coating film. In the case of a winding coil of a small-sized motor, it is necessary that the end thereof is connected electrically and mechanically to each commutator leg, but conventionally, the melting point of the commutator leg and that of the copper wire material are almost the same, and an insulating coating film exists, and therefore, the inside surface of the bent commutator leg has been made to be an unsmooth surface where fine irregularities are made (so-called star marking: making small star-shaped recesses), and furthermore, heat shock has been applied by spot welding to perform the coating film separation and the connection. However, this method is a factor to cause breaking of the wire, and therefore, as shown in FIG. 4, the breaking of the wire because of the heat shock has been moderated in such a way that solder plating is applied to the bent inside part of the commutator terminal in advance to hold the copper wire material.
However, as mentioned above by referring to FIG. 7, there has been such a problem that when soldering the varistor 21, the solder on the inside of the bent commutator leg is also melted by the heat thereof, and after that, at the time of cooling and solidification, the bent tip part is opened. This is caused for the reason that the amount of solder is larger on the varistor connection side, and furthermore, the spring back of the bent part also acts to pull the bent tip part of the commutator terminal to the varistor side on the outside at the time of solder cooling.
Furthermore, there is also such a problem that by the heat at the time of spot welding or soldering, the insulating coating film may be burnt to produce a poisonous gas, so that the need for the environmental countermeasure is produced. Moreover, the solder is a heavy metal, and the need for the environmental countermeasure is wanted to the soldering itself.
Therefore, it is an object of the present invention to solve such problems, so that the reduction of defectives of breaking of the wire because of heat shock at the time of welding is achieved in the connection between the commutator leg and the copper wire material of a small-sized motor, and in the meantime, to make it possible to select the most suitable one as the material to be welded to the copper wire material regardless of many kinds of materials of the commutator leg used for the motor commutator, so that the stabilization of welding is achieved, and the reliability of connection is increased.
Furthermore, it is an object of the present invention to eliminate the need for the solder plating and star marking to simplify the work process in the connection between the commutator leg and the copper wire material of a small-sized motor.
Furthermore, it is an object of the present invention to provides rotor for a small-sized motor wherein the solder plating is eliminated, and furthermore, a poisonous gas from the insulating coating film because of heat is restrained to correspond to the environment.
The rotor for a small-sized motor of the present invention has a plurality of rotor magnetic poles and a commutator on a rotor shaft, and both ends of a wire of each winding of the above described rotor magnetic poles are tied up with and connected by welding to a commutator leg connected to the corresponding commutator piece end of the commutator, respectively. The commutator leg has a copper-based base material, and is composed by attaching a thin layer of a clad material with a lower melting point and higher electric resistance than that of the above described base material on that at least at a portion of the surface part with which the winding wire comes into contact for welding.
Furthermore, in the method of manufacturing a rotor for a small-sized motor, a plurality of rotor magnetic poles and a commutator are mounted on a rotor shaft, and both ends of a wire of each winding of the above described rotor magnetic poles are tied up to the commutator leg connected to the corresponding commutator piece end of the commutator, and after that, they are heated by welding and connected. A copper-based base material is prepared, and a clad material with a melting point lower than that of the above described base material and a high electric resistance is attached to the base material at least at a portion of the surface part with which the winding wire comes into contact for welding. The commutator leg is formed by this base material to which the clad material is attached.